1. Field of the Invention
The present invention relates to a profile correction apparatus for correcting a color profile defining a coordinate conversion among a plurality of color spaces, and a profile correction program storage medium storing a profile correction program which causes a computer to operate as the profile correction apparatus when the profile correction program is incorporated into the computer.
2. Description of the Related Art
Recently, computerization and digitalization advance in a printing field too. For example, in the event that a printed matter of a color image is produced, image data is generated in such a matter that the color image is read by a color scanner to obtain image data (CMY data) representative of three colors of, for example, cyan (C), magenta (M), and yellow (Y), and color images represented by the obtained image data are edited on a display screen, so that image data representative of the edited color image is created. The image data thus created are created in form of image data (CMYK data) representative of four colors of, for example, cyan (C), magenta (M), yellow (Y), and black (K). Machine plates, which carry halftone dot images for those four colors, respectively, are created in accordance with the image data. The machine plates thus created are mounted on a printing machine so that the halftone dot images of CMYK four colors are printed in such a manner that those halftone dot images are superposed on one another. Thus, there is produced a printed matter of the color image consisting of those halftone dot images. A system for creating a printed matter upon receipt of CMY data after editing is referred to as a printing system hereinafter.
This printing system is a sort of image output system wherein first image data in which a color of a color image is represented in a first color space is converted into second image data in which a color of a color image is represented in a second color space, and a color image is outputted in accordance with the second image data. The conversion of the image data, which is performed by the image output system, is a conversion taking notice of colors as will be described later, and is referred to as a color conversion. A portion for implementing the function of the color conversion in the image output system is referred to as a color conversion section. A portion of outputting a color image in accordance with the image data after the color conversion in the image output system is referred to as an image output section. In the above-mentioned printing system, an image setter to a printing machine is the image output section.
In the printing field, as another sort of the image output system, there is known a proof system wherein a color image in a printed matter is reproduced by a high-performance printer capable of creating a halftone dot structure. According to the proof system, the CMY data after editing is converted into image data for a printer so that the high-performance printer outputs a color image represented by the image data. According to the proof system, the image output section comprises a printer.
It is known that an ability of the image output section incorporated into the image output system for outputting a color image changes with the passage of time, and colors of the color image also changes with the passage of time. For this reason, even if there are constructed a printing system capable of outputting a color image edited on a display of an editing apparatus with a faithful color and a proof system capable of exactly reproducing a color of a printed matter, a color of the color image outputted will change to a color different from the original color with the passage of time.
In order to obtain a color image of the original color through correction of the change with the elapse, hitherto, a structure of halftone dots constituting the color image is corrected. However, a scheme of creating a structure of halftone dots is varied in accordance with a maker of an image output section that is incorporated into an image output system. For this reason, even if there are developed correction algorithm and correction program capable of correcting the change with the elapse in the image output section of a specified maker, it is difficult to introduce the correction algorithm and the like into the image output section of another maker, and it is low in general-purpose properties.
By the way, it is known that even if the second data is the same image data, for example, (C, M, Y, K)=(50, 50, 100, 100), a color of a color image, which is outputted by the image output section in accordance with the image data, is varied in accordance with a type of an apparatus constituting the image output section. The color conversion section of the above-mentioned image output system converts the first image data representative of a certain image into the second image data according to the image output section in order to remove the difference of a color. The conversion (the color conversion) from the first image data to the second image data is considered as the coordinate conversion among a plurality of color spaces. This color conversion is adopted, not restricted to the printing field, in order to unify colors of color images among a plurality of sorts of apparatuses such as scanners and displays. Generally, in such a color conversion, there is adopted a color profile in which the above-mentioned coordinate conversion is defined by a LUT (Look Up Table) format and the like. Further, as a color profile used in the color conversion, generally, there is adopted a united form of color profile such as an ICC profile.
In view of the foregoing, as a method of removing the above-mentioned change with elapse, there is considered a method of making over again the color profile. According to this method, in the event that a maker of a certain image output system develops a creating algorithm for making over again a color profile, it is easy to introduce the creating algorithm into the image output system of another maker, and it is high in general-purpose properties.
However, to create the color profile, there is a need that an image output system outputs a large number of color patches, and a colorimeter measures colors of the color patches. Such a measure is very troublesome. While there is a colorimeter for automatically measuring a color patch, such a colorimeter is expensive, and it is difficult for a user of the image output system to possess the colorimeter for the purpose of correction of change with elapse in the image output system. Thus, it is desired to develop a profile correction apparatus capable of correcting a color profile without spending a great deal of time and effort.
Such a profile correction apparatus is desired in not only a printing field, but also the whole fields using the image output system involved in change with elapse.